White balance (WB) adjustment is a known processing in which a gain with respect to a color signal of each pixel forming digital image data is changed to provide image data having an appropriate color tone. Digital cameras are provided with an internal WB adjusting function for computing a WB gain in accordance with the user's setting before image capturing, thereby performing WB adjustment with respect to image data obtained by the image capturing. With regard to the WB gain computation, a large number of techniques have conventionally been proposed, including those disclosed in Japanese Patent Laid-Open Publications Nos. 2001-112019, 2000-92509, and 2003-327744.
In general, image data which has been subjected to compression processing as well as such WB adjustment is recorded, as a compressed image file, on a recording medium which records captured image data. While the compressed image file has an advantage that it provides a user with ease in handling because of a small data amount, it suffers from problems that the image quality is deteriorated due to the compression processing and that it is difficult to subject such a compressed image file to further image correction. In particular, while the WB adjustment is generally performed using the user's setting at the time of image capturing, there are instances where such user setting is not appropriate. In such instances, if the user attempts to perform further WB adjustment with respect to the compressed image using different setting, the image quality would be deteriorated.
In order to address the above problems, in recent years, cameras provided with a white balance bracketing function for creating a plurality of compressed image files subjected to different WB adjustment processes by a single image capturing operation have been known.
In addition, digital cameras which record RAW data obtained by digitizing an image capturing signal are also known. As the RAW data is image data which is not subjected to compression processing or WB adjustment, further WB adjustment can be performed without deterioration of the image quality.
When outputting such RAW data, the WB gain of the RAW data is recorded as well. Recording of the WB gains enables WB adjustment to be performed easily by an external image processing apparatus. The above-described Japanese Patent Laid-Open Publication No. 2003-324744 discloses that both color gain information based on the setting at the time of image capturing and color gain information for manual white balance which has been adjusted by assuming the image capturing under a variety of light sources is recorded with regard to one RAW data item. By recording a plurality of WB gains with regard to a single RAW data item in this manner, it is possible to perform appropriate WB adjustment even if the WB setting at the time of image capturing is erroneous.
When performing white balance bracketing, however, it is naturally necessary to compute a plurality of WB gains with regard to a single image data item. In a case where a plurality of WB gains are recorded with regard to one RAW data item as disclosed in the above-described Japanese Patent Laid-Open Publication No. 2003-324744, it is similarly necessary to compute a plurality of WB gains. In this case, there has been a problem that it takes a long time to compute a plurality of WB gains in accordance with a WB gain computation technique which has been proposed conventionally.
It is therefore an advantage of the present invention to provide a digital camera in which a plurality of WB gains can be computed in a short time and a gain computation method.